Driver lines that direct Cre protein to specific neuron types have proven to be invaluable tools to not only visualize specific neuron types but also to manipulate their activity through the Cre- mediated activation of optogenetic probes or to assess gene function by Cre-mediated gene knockout. Most Cre driver lines, such as BAC-based Cre drivers or knock-ins of Cre into specific loci, monitor the complete expression pattern of entire genetic loci. However, very few genes are exclusively expressed in very small populations of specific neuron types and this lack of cellular specificity limits the use of these driver lines. W propose here to develop transgenic mouse driver lines that direct Cre expression to very restricted numbers of neuronal cell types in different regions of the mouse brain, thereby providing tools to precisely map their function and molecular composition. To achieve this aim, we aim to test the hypothesis - built from our past work in the nematode C.elegans - that the cis-regulatory control elements of the mouse loci that encode the vesicular transporters for the four main neurotransmitter systems in the vertebrate central nervous system, glutamate and -aminobutyric acid (GABA) and acetylcholine (ACh) are composed of a modular assembly of individual, highly cell type-specific cis-regulatory elements. We will experimentally test the hypothesis that the expression of individual, isolated cis-regulatory elements may subdivide cholinergic, glutamatergic and GABAergic domains into restricted and perhaps novel domains of the mouse central nervous system and thereby constitute reproducible and highly specific drivers for directing the expression of genes that allow the genetic manipulation of neurons and neuronal circuits. This cis-regulatory dissection approach may solve the specificity problem of most currently available driver lines that are unable to exclusively target restricted numbers of cells.